--- name: "ioctl_xfs_commit_range" section: "2" platform: "linux" package: "xfsprogs" version: "7.2.1-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/ioctl_xfs_commit_range" --- # ioctl\_xfs\_commit\_range(2) conditionally exchange the contents of parts of two files ioctl\_xfs\_start\_commit - prepare to exchange the contents of two files ## NAME ioctl\_xfs\_commit\_range - conditionally exchange the contents of parts of two files ioctl\_xfs\_start\_commit - prepare to exchange the contents of two files ## SYNOPSIS **#include \**\ **#include \** **int ioctl(int** *file2\_fd***, XFS\_IOC\_START\_COMMIT, struct xfs\_commit\_range \****arg***);** **int ioctl(int** *file2\_fd***, XFS\_IOC\_COMMIT\_RANGE, struct xfs\_commit\_range \****arg***);** ## DESCRIPTION Given a range of bytes in a first file **file1\_fd** and a second range of bytes in a second file **file2\_fd**, this [**ioctl**(2)](/ioctl/2.md) exchanges the contents of the two ranges if **file2\_fd** passes certain freshness criteria. Before exchanging the contents, the program must call the **XFS\_IOC\_START\_COMMIT** ioctl to sample freshness data for **file2\_fd**. If the sampled metadata does not match the file metadata at commit time, **XFS\_IOC\_COMMIT\_RANGE** will return **EBUSY**. Exchanges are atomic with regards to concurrent file operations. Implementations must guarantee that readers see either the old contents or the new contents in their entirety, even if the system fails. The system call parameters are conveyed in structures of the following form: ``` struct xfs_commit_range { __s32 file1_fd; __u32 pad; __u64 file1_offset; __u64 file2_offset; __u64 length; __u64 flags; __u64 file2_freshness[5]; }; ``` The field *pad* must be zero. The fields *file1\_fd*, *file1\_offset*, and *length* define the first range of bytes to be exchanged. The fields *file2\_fd*, *file2\_offset*, and *length* define the second range of bytes to be exchanged. The field *file2\_freshness* is an opaque field whose contents are determined by the kernel. These file attributes are used to confirm that **file2\_fd** has not changed by another thread since the current thread began staging its own update. Both files must be from the same filesystem mount. If the two file descriptors represent the same file, the byte ranges must not overlap. Most disk-based filesystems require that the starts of both ranges must be aligned to the file block size. If this is the case, the ends of the ranges must also be so aligned unless the **XFS\_EXCHANGE\_RANGE\_TO\_EOF** flag is set. The field *flags* control the behavior of the exchange operation. - **XFS\_EXCHANGE\_RANGE\_TO\_EOF** Ignore the *length* parameter. All bytes in *file1\_fd* from *file1\_offset* to EOF are moved to *file2\_fd*, and file2's size is set to (*file2\_offset*+(*file1\_length*-*file1\_offset*)). Meanwhile, all bytes in file2 from *file2\_offset* to EOF are moved to file1 and file1's size is set to (*file1\_offset*+(*file2\_length*-*file2\_offset*)). - **XFS\_EXCHANGE\_RANGE\_DSYNC** Ensure that all modified in-core data in both file ranges and all metadata updates pertaining to the exchange operation are flushed to persistent storage before the call returns. Opening either file descriptor with **O\_SYNC** or **O\_DSYNC** will have the same effect. - **XFS\_EXCHANGE\_RANGE\_FILE1\_WRITTEN** Only exchange sub-ranges of *file1\_fd* that are known to contain data written by application software. Each sub-range may be expanded (both upwards and downwards) to align with the file allocation unit. For files on the data device, this is one filesystem block. For files on the realtime device, this is the realtime extent size. This facility can be used to implement fast atomic scatter-gather writes of any complexity for software-defined storage targets if all writes are aligned to the file allocation unit. - **XFS\_EXCHANGE\_RANGE\_DRY\_RUN** Check the parameters and the feasibility of the operation, but do not change anything. ## RETURN VALUE On error, -1 is returned, and *errno* is set to indicate the error. ## ERRORS Error codes can be one of, but are not limited to, the following: - **EBADF** *file1\_fd* is not open for reading and writing or is open for append-only writes; or *file2\_fd* is not open for reading and writing or is open for append-only writes. - **EBUSY** The file2 inode number and timestamps supplied do not match *file2\_fd*. - **EINVAL** The parameters are not correct for these files. This error can also appear if either file descriptor represents a device, FIFO, or socket. Disk filesystems generally require the offset and length arguments to be aligned to the fundamental block sizes of both files. - **EIO** An I/O error occurred. - **EISDIR** One of the files is a directory. - **ENOMEM** The kernel was unable to allocate sufficient memory to perform the operation. - **ENOSPC** There is not enough free space in the filesystem exchange the contents safely. - **EOPNOTSUPP** The filesystem does not support exchanging bytes between the two files. - **EPERM** *file1\_fd* or *file2\_fd* are immutable. - **ETXTBSY** One of the files is a swap file. - **EUCLEAN** The filesystem is corrupt. - **EXDEV** *file1\_fd* and *file2\_fd* are not on the same mounted filesystem. ## CONFORMING TO This API is XFS-specific. ## USE CASES Several use cases are imagined for this system call. Coordination between multiple threads is performed by the kernel. The first is a filesystem defragmenter, which copies the contents of a file into another file and wishes to exchange the space mappings of the two files, provided that the original file has not changed. An example program might look like this: ``` int fd = open("/some/file", O_RDWR); int temp_fd = open("/some", O_TMPFILE | O_RDWR); struct stat sb; struct xfs_commit_range args = { .flags = XFS_EXCHANGE_RANGE_TO_EOF, }; /* gather file2's freshness information */ ioctl(fd, XFS_IOC_START_COMMIT, &args); fstat(fd, &sb); /* make a fresh copy of the file with terrible alignment to avoid reflink */ clone_file_range(fd, NULL, temp_fd, NULL, 1, 0); clone_file_range(fd, NULL, temp_fd, NULL, sb.st_size - 1, 0); /* commit the entire update */ args.file1_fd = temp_fd; ret = ioctl(fd, XFS_IOC_COMMIT_RANGE, &args); if (ret && errno == EBUSY) printf("file changed while defrag was underway\n"); ``` The second is a data storage program that wants to commit non-contiguous updates to a file atomically. This program cannot coordinate updates to the file and therefore relies on the kernel to reject the COMMIT\_RANGE command if the file has been updated by someone else. This can be done by creating a temporary file, calling **FICLONE**(2) to share the contents, and staging the updates into the temporary file. The **FULL\_FILES** flag is recommended for this purpose. The temporary file can be deleted or punched out afterwards. An example program might look like this: ``` int fd = open("/some/file", O_RDWR); int temp_fd = open("/some", O_TMPFILE | O_RDWR); struct xfs_commit_range args = { .flags = XFS_EXCHANGE_RANGE_TO_EOF, }; /* gather file2's freshness information */ ioctl(fd, XFS_IOC_START_COMMIT, &args); ioctl(temp_fd, FICLONE, fd); /* append 1MB of records */ lseek(temp_fd, 0, SEEK_END); write(temp_fd, data1, 1000000); /* update record index */ pwrite(temp_fd, data1, 600, 98765); pwrite(temp_fd, data2, 320, 54321); pwrite(temp_fd, data2, 15, 0); /* commit the entire update */ args.file1_fd = temp_fd; ret = ioctl(fd, XFS_IOC_COMMIT_RANGE, &args); if (ret && errno == EBUSY) printf("file changed before commit; will roll back\n"); ``` ## NOTES **Some filesystems may limit the amount of data or the number of extents that can** be exchanged in a single call. ## SEE ALSO [**ioctl**(2)](/ioctl/2.md)